The present invention relates to shaped articles which are composed of a synthetic copolymer containing fluorine groups and which, in their original state, are permeable to liquids and gases and are simultaneously oleophobic and oleophilic, and also to the use of shaped articles of this type. The invention also relates to processes for the preparation of these shaped articles and to processes for modifying their structure. The invention also relates to the use of the shaped articles.
Within the scope of the description of the present invention and of the claims, the term "shaped articles" is intended to embrace films and tubular structures, such as tubes and hollow fibers (capillaries). In accordance with the definition, the term "shaped articles" also embraces coatings.
Open-pore, microporous plastic films are known, for example, those composed of polyamide, polysulfone or polyvinylidene fluoride (U.S. Pat. No. 3,615,024), which are prepared in accordance with the so-called phase inversion process by casting a solution of a plastic to form a liquid film and coagulating the plastic dissolved in this solution to form the above microporous film of stable shape.
Open-pore films which are prepared by mixing polyvinylidene fluoride with polyvinyl acetate are also suggested in European Patent Application No. 0,012,557. Only when the film is finished is it subsequently converted by saponification into a mixture containing polyvinyl alcohol. Copolymers of tetrafluoroethylene and vinyl acetate or vinyl alcohol, which are hydrophilic/hydrophobic without further treatment, have hitherto not yet been employed as selectively permeable films.